Consider again the solution of CaCl2 and Mg(NO3)2 in which the concentrations of both Mg2+ and Ca2+ are the same, 0.01. M. When a concentrated NaOH solution is added drop wise, Mg(OH)2 begins to precipitate first. What is the concentration of Mg2+ ions when Ca(OH)2 just begins to precipitate? Choose the best answer. Again, for the sake of simplicity, assume that the precipitation reactions do not result in any change of the volume of the reaction mixture. The Ksp values of the calcium and magnesium hydroxides are 6.5 x 10-5 and 7.1 x 10-12, respectively.
a) > 10-6 M
b) < 10-6 M
c) < 10-7 M
d) < 10-8 M